Isolation, characterization and expression analyses of two cell wall invertase genes in maize

Acid invertases are glycoproteins that catalyze the hydrolysis of sucrose t o glucose and fructose and are associated with metabolic sink tissues in a variety of plant species. Acid invertases are divided into cell wall-bound invertases (INCW) and soluble invertases based on their location in the cel l. We describe here the isolation and characterization of two cell wall inv ertase cDNA (Incw1 and Incw2) and genomic clones. Since the deduced amino a cid sequences of Incw1 and Incw2 clones are more similar to carrot cell wal l invertases than they are to maize soluble invertase, we conclude Incw1 an d Incw2 represent cell wall-bound invertases. Both genomic clones have six introns and seven exons, typical of most other acid invertase genes. Incw1 mRNA is present in cell suspension culture, etiolated shoots, roots and, at much reduced steady state levels, in developing endosperm. In contrast, In cw2 mRNA is present in shoots and developing endosperm, but lacking in root s and the miniature1 (mn1-1) mutant endosperm. In situ hybridization studie s show that the Incw2 mRNA is confined to the basal endosperm transfer cell s in a developing kernel.